The present invention relates to an electric contact probe assembly which is suitable for use in various sockets for electrically testing semiconductor-related products and probes for wafer tests and burn-in tests of wafers.
Electric contact probe assemblies of various structures are used for electrically testing conductive patterns of printed circuit boards and electronic component parts (such as oven accelerated aging tests, environment tests and burn-in tests), and as a part of contact probes for testing semiconductor wafers and sockets (including those for permanent use) and connectors for semiconductor devices (which may be in LGA, BGA, CSP and bear chip packages).
The signal frequency that needs to be handled by such sockets for semiconductor devices may reach the level of several hundred MHz with the recent demand for high frequency semiconductor devices. Therefore, the sockets that are used for such high speed semiconductor devices are required to use electric contact probe assemblies demonstrating correspondingly low inductance and low electric resistance. To achieve such a goal or the reduction in the inductance and electric resistance, the applicant of this application previously proposed in Japanese patent application No. 8-188199 to use,a coil end of a coil spring as a probe member for engagement with the object to be contacted so as to integrate the probe member with the compression coil spring.
As mentioned earlier, in the case of an electric contact probe assembly using a coil-shaped resilient probe member consisting solely of a coil spring, because the connection between the coil spring and the probe member requires no length at all, a low-profile design is possible particularly when a plurality of electric contact probe assemblies are arranged one next to the other, and the performance in high frequency ranges can be improved. However, when the electric contact probe assemblies are provided on a circuit board (such as those for relaying signals to a test circuit), because an end of each coil spring is required to be attached to the corresponding terminal of the circuit board by soldering or the like, the handling of the assembly is becoming more and more difficult with the demand for an ever smaller spacing between adjacent electric contact probe assemblies.
This trend also results in the restriction on the selection of the solder that can be used for such soldering work. For instance, when soldering a coil end of a coil-shaped resilient probe member to a circuit board such as a test mother board, the soldering procedure using a mask which is commonly used in connection with printed circuit boards may not be satisfactory because the solder may rise up to a coarse turn section of the extremely small coil-shaped resilient probe member due to the capillary effect Therefore, a special soldering procedure may become necessary so as to accurately control the solder thickness, and this inevitably complicates the soldering work.
Also, when a plate-shaped housing is used which is provided with holder holes each receiving a coil-shaped resilient probe member so as to project a coil end, the soldering work must be carried out so as to prevent the coil-shaped resilient probe members from dropping off from the corresponding holder holes, and this complicates the structure of the assembly.
In view of such problems of the prior art, a primary object of the present invention is to provide an electric contact probe assembly which is suited for a high density design while simplifying the fabrication process.
A second object of the present invention is to provide an electric contact probe assembly which is suited for a high density design and provides a favorable high frequency performance.
A third object of the present invention is to provide an electric contact probe assembly which demonstrates low electric resistance.
A fourth object of the present invention is to provide an electric contact probe assembly which is economical.
According to the present invention such objects can be accomplished by providing an electric contact probe assembly, comprising: a non-electroconductive support sheet having a front and reverse sides and at least one through hole; an electroconductive patch attached to a part of the support sheet adjacent to the through hole; an elecroconductive resilient probe member having a base end attached to the patch and a free end projecting from the front side of the support sheet; and a circuit board placed over the reverse side of the support sheet and having a circuit layer incorporated therein and a terminal facing the reverse side of the support sheet; the support sheet being fixedly attached to the circuit board by an electroconductive bonding member which both physically and electrically connects the patch with the terminal.
Because the resilient probe member is integrally incorporated in the support sheet, the resilient probe member can be handled via the support sheet, and this is particularly significant when a large number of resilient probe members are arranged on a single support sheet in the form of a sheet. The support sheet allows the through holes to be formed without any difficulty, and by fixedly attaching an electroconductive patch to the support sheet so as to align with the through hole, not only the support sheet can be physically attached to the terminal of the circuit board with the electroconductive bonding member such as solder, brazing material or an electroconductive bonding agent filled in the through hole but also the resilient probe member can be electrically connected to the terminal via the electroconductive member. The absence of any intervening element in the path of electric connection contributes to the improvement of the high frequency performance.
If the resilient probe member consists of a coil spring, and one of the coil ends of thereof is fixedly attached to the electroconductive patch, the electric contact probe assembly can be easily formed by using such a coil spring. If the one coil end is defined by a plane extending perpendicularly to the axial line of the coil spring, the perpendicularity of the coil-shaped resilient probe member can be ensured without any difficulty, and the assembling work is simplified.
If the other coil end of the coil spring is provided with a small diameter turn adapted to be received within a remaining part of the coil spring when the coil spring is axially compressed, the contact area for the object to be contacted is enlarged, and a concentration of the load can be avoided. In particular, when contacting the coil end with a solder ball or the like, the denting of the solder ball or the like can be avoided.
A housing layer may be placed over the front side of the support sheet, the housing layer defining a holder hole through which a free end of the compression coil spring projects, so that the lateral collapsing of the coil-shaped contact probe member may be avoided. An end of the holder hole remote from the support sheet may be provided with an internal flange which controls a projecting length of the free end of the compression coil spring. The contact probe member may also consist of a cantilever sheet spring.
According to a preferred embodiment of the present invention, the patch is attached to the front side of the support sheet so as to expose at least a part of the patch to the interior of the through hole. The patch may entirely cover the through hole, and may be provided with a central opening which allows an automatic adjustment of the electroconductive bonding member.
The patch may also be attached to the reverse side of the support sheet so as to expose at least a part of the patch to the interior of the through hole. Such an embodiment allows the thickness of the assembly to be minimized. For the convenience of retaining the base end of the coil-shaped contact probe member, the patch may include an axial projection which extends into the through hole. The axial projection typically consists of an annular or cylindrical projection so that the base end of the coil-shaped probe may be fitted onto or into the projection.
The electric contact probe assembly can be fabricated by a method comprising the steps of: preparing a non-electroconductive support sheet having a front and reverse sides and at least one through hole; attaching an electroconductive patch to a part of the support sheet adjacent to the through hole; attaching a base end of an electroconductive resilient probe member to the patch so as to cause a free end thereof project from the front side of the support sheet; preparing a circuit board having a circuit layer incorporated therein and a terminal exposed on one side thereof; depositing an amount of soldering or brazing material on at least one of the patch and the circuit board terminal; placing the circuit board over the reverse side of the support sheet with the terminal directly opposing the patch; and melting and resolidifying the soldering or brazing material so as to connect the patch and the circuit board terminal together both electrically and physically.